<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            width: 100%;
            height: 100%;
        }
        .content{
            width: 100%;
            height: 4000px;
            background: url("../img/mooc.png") center top no-repeat;
        }
        /*.opacity{*/
            /*width:100%;*/
            /*height: 100%;*/
            /*background: url("");*/
            /*position: fixed;*/
            /*left:0px;*/
            /*top: 0px;*/
            /*z-index: 0;*/
        /*}*/
        .login{
            width: 360px;
            height: 360px;
            background: url("../img/login.png");
            z-index: 2;
            position: fixed;
            left:50%;
            top: 50%;
            margin-left: -180px;
            margin-top: -180px;
        }
    </style>
</head>
<body>
    <div class="content"></div>
    <div class="opacity"></div>
    <div class="login"></div>
</body>
</html>